Strip casting means the production of a cast strip (which term also includes a sheet) by pressing a melt between a travelling belt, which belt, via solidifying melt, makes contact with part of the periphery (the casting region) of a casting drum rotating along with the belt so that the casting region moves continuously around the periphery of the drum during the casting process.
Melt can, for example, be fed continuously into a V-shaped cleft formed between the casting drum and the travelling belt in a tangential direction as the belt enters the casting region. The belt leaves the casting drum tangentially at the downstream end of the casting region and supports the cast strip in its movement away from the drum.
The thickness of the cast strip is determined by several factors, the most important being the following:
The depth of the melt formed in the V-shaped cleft. PA1 The composition or alloying of the melt. PA1 The temperature of the melt. PA1 The speed of the travelling belt and the peripheral speed of the casting drum. PA1 The prestress in the travelling belt. PA1 The elasticity of the travelling belt. PA1 The degree of cooling of the casting drum and PA1 the travelling belt.
The quality characteristics of the cast strip are also dependent on the above-mentioned factors to a large extent. In addition, it has been shown that the quality of the strip is to a very large extent dependent on whether the peripheral speed of the casting drum exactly matches the speed of the belt. For the best quality casting, there must be no slipping between the strip to be cast, and the casting drum and between the strip to be cast and the travelling belt, respectively. If the respective speeds are different, the cast strip during the casting and solidification process is subjected to an internal stress between the layer which makes contact with the drum and the layer which makes contact with the belt. The direction of this stress is dependent upon which is greater: the speed of the belt or the peripheral speed of the drum.
The above-mentioned internal stresses give rise to the formation of cracks and to some degree of brittleness in the as-cast strip both of which faults may make the cast material unsuitable for further processing.
Several different principles for driving the travelling belt and the casting drum have been tried. One method involving a fixed gear changed between a drive means for the belt and the drum has proved to function very badly, especially if cast strips of different alloys and thicknesses are to be produced with the same equipment.
Different embodiments of the "master-slave" principle, in which, for example, the drive means for the travelling belt has been selected for determining the casting speed and in which the drive means of the casting drum has been designed so as to follow the main drive in the best possible way, have also been tried but have also been shown to give rise to problems.